core: load stmm via secure partition

Secure variable storage for EFI variables is critical for enabling and
protecting UEFI Secure Boot. Unfortunately due to the fact that SPD and
SPM are mutually e

core: load stmm via secure partition

Secure variable storage for EFI variables is critical for enabling and
protecting UEFI Secure Boot. Unfortunately due to the fact that SPD and
SPM are mutually exclusive, we can't run StMM from EDK2 and OP-TEE.
An advantage of doing so is that different firmware implementations
can leverage EDK2's StandAloneMM and in cooperation with OP-TEE RPMB
APIs can store UEFI variables in a secure storage.
This makes the variable storage quite generic in any device with an RPMB
partition.

Using a well debugged application is preferable over rewriting the whole
application as a TA. Another advantage is that this inherits the Fault
Tolerant Writes (FTW) functionality built-in on StMM to protect
variables against corruptions during writing. Considering the FFA
changes of the future Arm architectures using an SP that includes
everything seems like a better choice at the moment.
The 'SPM emulation' currently added into OP-TEE only supports
a single SP to be launched. This means that the StMM embedded
application has the RPMB driver built in at the moment. In the future we
can add code (evolving FFA) to launch multiple SPs. So the StMM variable
handling can be decoupled from the RPMB driver, which will reside in a
different SP.

So let's add a user mode secure partition context and support loading
"Standalone MM" of EDK2 into it. A separate syscall handling is added to
serve as different kind of ABI and syscall IDs. The secure partition has
a TA like interface towards normal world, but requests are routed into
the StMM partition instead.

CFG_STMM_PATH is assigned the path of BL32_AP_MM.fd, for instance:
CFG_STMM_PATH=...Build/QemuVirtMmStandalone/DEBUG_GCC5/FV/BL32_AP_MM.fd

Since this is quite tricky to compile and test you can use this [1].
Just clone the repo and run ./build.sh. The script will pick up edk2,
edk2-platforms, op-tee, atf and U-boot and compile all the necessary
binaries for QEMU. A patch (awful hack) has been added to U-boot to
allow RPMB emulation through it's supplicant, since QEMU RPMB emulation
is not yet available.
After compiling and launching QEMU the usual U-boot commands for EFI
variable management will store the variables on an RPMB device.

[1] https://git.linaro.org/people/ilias.apalodimas/efi_optee_variables.git/

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Co-developed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Co-developed-by: Pipat Methavanitpong <pipat1010@gmail.com>
Signed-off-by: Pipat Methavanitpong <pipat1010@gmail.com>
Co-developed-by: Miklos Balint <Miklos.Balint@arm.com>
Signed-off-by: Miklos Balint <Miklos.Balint@arm.com>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-by: Etienne Carriere <etienne.carriere@linaro.org>

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